kWH readings upon charging

Battery longevity is achieved by never operating at extremes.

For Prius PHV, that means "full" is actually 85% and "empty" is 23% for usable EV capacity.

I'm not sure what the range is for Prime, since my delivery wait is not over yet...

 

As John said, 0 miles is not zero State of Charge and full charge is not 100% SOC, there are buffers both sides.
If we take EPA official scores we can have an idea of the usable portion of the battery charge: on the test the prime moved 25 miles EV while consuming (from wall) 25.3 kWh per 100 miles (EPA rounded it to 25), so, 25*25.3/100=~6.3 kWh from the wall.
There are charging losses, actual charge into the battery will depend on those losses, example: if charging losses are 15% then 6.3*0.85=~5.3 kWh accumulated in the battery.

 

This is exactly right, but it also implies that the Prime average about 212 Wh/mile over the 5 cycle EPA test.

I know that the Prime is an exercise in efficiency, but I have trouble accepting it is *that* efficient. Even 225 Wh/mile is amazing.

 

If the 212 Wh/mile you mention is 'from battery' after 15% charging losses, please bear in mind that Toyota claimed they have improved charging efficiency with the Prime (to 90%?) so it could be 0.253*0.9=0.228 Wh/mile from battery in the EPA 5 cycle test.

 

The Prime is also a hybrid, so it needs to also save charge in the battery for hybrid mode in addition to having buffers for longevity.

Published EPA ratings are from the wall, so include charging losses.

 

In the case of the EPA -- assumed charging losses

 

Yep. Do you happen to know if they assume worse case?

 

I've been told that they use a generic L2 charger. I vaguely recall 13% charging losses. Sorry I cannot be more certain.

 

L2 would be about best case. L1 is generally worse in terms of charging efficiency.